While much human diversity arose through genetic drift, it is increasingly clear that different human populations have distinctly adapted to the environments they encountered in the 100,000 years since our species left its east African birthplace. Today, some of these genetic adaptations account for inherent inter-individual differences in disease risk through different phenotypic response to identical environmental conditions. Here I propose to better understand this phenomenon by studying the separate adaptations to different temperatures that have occurred in the model species Drosophila melanogaster since it also left its African home and spread across the planet. In particular, I wil study how temperature affects developmental timing, a quantitative polygenic trait, and how different D. melanogaster populations have adapted to mitigate temperature's effects on development.